What Affects Pregnancy Test Accuracy?

Today’s home pregnancy tests can be nearly 100% accurate – if you follow directions precisely and use the test at the right time. While following instructions is not necessarily a problem, the timing of the test often is.

Women who are trying to conceive are anxious to know just how early they can perform the test and expect accurate results.

Just how early the test can be taken depends on a few factors. The first is how long ago ovulation occurred. And if conception did in fact take place, when the fertilized egg implanted.

In addition the brand of pregnancy test is a factor, because not all are equally sensitive – though they are quite accurate overall at detecting hCG (the pregnancy hormone) in even tiny amounts.

Ovulation occurs when the ovary releases an egg. The egg enters the fallopian tube, and will live for only 12 to 24 hours unless fertilized. Because sperm can live from 3 to 5 days, the chance of fertilization is increased if there is sperm already present in the tube.

After fertilization, the egg will remain in the fallopian tube for several days, dividing over and over again to form a multi-celled zygote. After descending into the uterus, the fertilized egg will implant in the rich lining of the uterus.

The body will not know it is pregnant until this implantation occurs, signaling the corpus luteum to maintain the uterine lining until the placenta is formed. hCG production begins and can be detected about a day after implantation.

This means it can take between 3 and 10 days total (usually between 5 and 7) after ovulation, for pregnancy hormone to be present. However, the levels of hCG are extremely low at first, though they do double every other day. It is this hormone which causes pregnancy symptoms.

In general, if the fertilized egg has an “early” implantation, it is possible to see a positive result on your home pregnancy test at day 7 post-ovulation. A more realistic expectation is to see the positive at day 9 or later, though less-sensitive tests may not give you results until nearly 14 days post ovulation.

And some women may not produce enough hormone to register a positive result until 17 days, or more.

So, when deciding when to use a home pregnancy test, keep this information in mind and be aware that due to the time between fertilization and implantation, and the time it takes to produce enough hCG for detection, it is possible to first have a negative result, followed by a positive one.

This can result in confusion and anxiety, especially if you are trying to become pregnant and think you have failed to conceive. In general, the best guideline is to wait until your period is late.